1. Field of the Invention
The present invention refers to a method for operating a transport assembly in the form of a long stator linear motor through which a plurality of transport units are moved along a transport path, wherein the movement of the transport units along the transport path is adjusted by setting setpoints of movement by at least one transport unit control.
2. Discussion of Background Information
Long stator linear motors are often used as flexible transport assemblies in production plants, machining plants, assembling plants and similar plants. A long stator linear motor is notoriously essentially composed of a long stator formed by a plurality of successively positioned driving coils and a plurality of transport units with excitation magnets (permanent magnets or electromagnets), which are moved along the long stator by energizing the respective driving coils with an electric current. The driving coils generate a moving magnetic field, which interacts with the excitation magnets on the transport units, in order to move the transport units. The long stator therefore forms a transport path, along which the transport units may be moved. Therefore it is possible to control the movement (position, velocity, acceleration) of each transport unit individually and independently from one another. To this end, each driving coil is controlled by an associated driving coil controller, which can obtain settings for moving a transport unit (for instance in the form of setpoints for position or velocity) from a superordinate plant control unit. Switches for the long stator linear motor may be provided along the transport path. The long stator is often formed by transport segments, wherein each transport segment forms a portion of the transport path and contains a number of driving coils. Usually a segment control is provided for a transport segment, which controls all driving coils of the transport segment. The design of the long stator linear motor, i.e. for instance the design of the driving coils, the transport path, the transport units, the guides of the transport unit, etc., and the control principle may obviously vary, wherein however the basic operating principle of a long stator linear motor remains the same.
A transport assembly provided in the form of a long stator linear motor may become complex, with a plurality of transport segments, which may also be connected to each other by means of switches. A great number of transport units may also be simultaneously moved on the same. Such a transport assembly therefore imposes high requirements on the control of the movement of individual transport units. In particular, normally, provisions have to be taken in order to avoid that single transport units do not collide during their movement.
U.S. Pat. No. 8,863,669 B2 describes a transport assembly, for example, which is formed by a long stator linear motor with a control of movement of transport units. The transport path is divided into zones, wherein a transport unit is controlled in a setpoint based zone based on a setpoint setting, and in a limit value based zone by means of settings for end position and maximum values of velocity and acceleration. In the limit value based control, these settings are transformed into a movement profile, according to which the transport unit is moved. U.S. Pat. No. 8,863,669 B2 also indicates that collisions of transport units have to be avoided, wherein no indication is provided on how this control is achieved.
In the same way, along the transport path barriers may be provided, which cannot be overridden by a transport unit. Such barriers may be real, physical barriers, such as, for example, the end of a transport segment, or logical barriers, for instance a switch, which is simultaneously occupied by another transport unit, or a transport segment in which there is no space for a further transport unit. Barriers may also be imposed, according to application, even temporarily, by the higher level plant control unit. Also barriers may not be overridden by the transport units during operation.
Not least, along the transport path local speed limits may be imposed, which may not be violated by a transport unit, for example a maximum speed in a curve, in order to avoid exceeding a maximum allowable centrifugal force.